February 10, 2005

Safe and Sound on Mars: Part II

by ssavage

What challenges might arise beyond the logistics of getting to Mars? Weather and biology might face astronauts working within an extended stay mission.

Astrobiology Magazine -- The National Research Council was tasked with evaluating the risks of landing humans safely to work on Mars. Their report highlights a number of unique aspects in transit to the red planet, as well as once humans step out onto the surface.

In this first of two parts summarizing some key points, their report goes beyond the logistics and looks at the novel weather and biology that might face astronauts working within an extended stay mission.

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The physical environments that might pose risks to crew safety on Mars fall into three categories: geologic, atmospheric, and radiation. The geologic features of interest in this study are airborne dust, regolith, and terrain. The two Viking landers were enveloped in a global dust storm soon after landing, and dust devils have been observed many times on Mars by Viking orbiters and landers, the Mars Pathfinder, and the Mars Global Surveyor.

Windblown dust appears to be a common condition on Mars and would cause electrostatic charging of astronauts' space suits during operations on the surface of Mars, as well as of their equipment and habitat. Despite this phenomenon, there has been no report of electrostatic damage to delicate electronics on any of the surface systems. Furthermore, neither the Viking missions nor the Mars Pathfinder mission experienced any problems due to electrostatic charging.

Objects on moist ground on Earth are said to be grounded since the conducting ground has an almost unlimited capacity to accept either positive or negative charge without changing its electric charge potential from what is essentially zero. Such natural discharge or prevention of charging is not expected to occur on Mars, because there is no near-surface liquid water.

The hazards from electrostatic discharge on Mars can range from a simple spark, equivalent to feeling a sting here on Earth after walking on certain types of carpet and reaching for a doorknob, to potentially more potent bursts between astronauts and large equipment or structures on Mars. The dry conditions and uncertainty about conductivity, charging, and discharging rates in the Mars environment create uncertainties about electrostatic effects on human operations in the Mars environment.

It would be helpful for NASA to investigate the design considerations and procedures used at the Siple research station in Antarctica, where there is little to no local electrical ground. Again, as an example of potentially innovative design solutions, two crossed-dipole antennas at Siple, each 21.4 kilometers long, occasionally charged up to the order of 20,000 volts when windborne ice particles passed over them. The danger of discharge was removed by connecting the antennas to the station buildings.

The buildings prevented a charge from accumulating on the antenna conductors by acting as large capacitors that stored the charge. The electrostatic voltage on the antennas was reduced to near zero, and since ice is not a perfect electrical insulator, the charge on the buildings dispersed gradually. Sharp conducting points, the needlelike devices referred to above, were also used near the buildings to bleed off the electrical charge.

The strongest surface winds observed by in situ measurements on Mars are believed to be 30 to 50 meters per second (67 to 111 miles per hour) based on eolian deposits at the Viking I landing site. From a terrestrial perspective, these wind speeds appear to represent a significant hazard. However, when the lower atmospheric dynamic pressure on Mars, resulting from a less dense atmosphere than on Earth, is accounted for, the Earth-equivalent wind speeds are much less.

Simply stated, the wind must blow nine times faster on Mars than here on Earth to achieve the equivalent dynamic pressure. In the strongest wind case mentioned above, a 30 to 50 meter per second (67 to 111 mile per hour) wind on Mars is roughly equivalent to a 3.3 to 5.5 meter per second (7.4 to 12 mile per hour) wind on Earth.

The Martian atmosphere has been determined to be composed predominantly of carbon dioxide (95 percent), with nitrogen, argon, and oxygen (all nontoxic) present in abundances greater than 0.1 percent.

Astronauts are by definition radiation workers. Radiation exposure in space will be a significant and serious hazard during any human expedition to Mars. The radiation dose received by astronauts on the surface of Mars will be a significant fraction of the total radiation exposure for the mission.

Strong oxidants detected in Martian soil by the Viking biology experiment would be inactivated by humidification inside the astronaut habitat. It is therefore essential that NASA implement proper humidification in conjunction with the filtration system as part of habitat atmosphere conditioning.

Even if strong oxidants are present, if the dust level is maintained at 1 mg/m3 or less and appropriate humidification systems are in place, there will be negligible risk associated with oxidation on the Martian surface.

The probability that life-forms exist on the surface of Mars (that is, the area exposed to ultraviolet radiation and its photochemical products) is very small. However, as a previous [1997] NRC study notes, there is a possibility that such life-forms exist there "in the occasional oasis," most likely where liquid water is present, and, furthermore, that "uncertainties with regard to the possibility of extant Martian life can be reduced through a program of research and exploration."

It is highly unlikely that infectious organisms are present on Mars. The same NRC study that focuses on the possibility that Martian organisms could be agents of infectious disease also states as follows: "The chances that invasive properties would have evolved in putative Martian microbes in the absence of evolutionary selection pressure for such properties is vanishingly small. Subcellular disease agents, such as viruses and prions, are biologically part of their host organisms, and an extraterrestrial source of such agents is extremely unlikely."

In light of experience gained during Apollo missions to the Moon, a previous [1993] NRC report concludes, "It would, however, be virtually impossible to avoid forward-contamination of Mars or back-contamination of Earth from human exploration." As such, NASA should ensure proper quarantine or decontamination of equipment that may have been exposed to a Martian life-form.